Afocal zooming optical system

ABSTRACT

An afocal zooming optical system includes a plurality of lens groups or components, in which some of the lens groups movable along the optical axis for zooming are included in the dioptry adjusting lens groups movable for dioptry adjustment, with others of the lens groups movable for zooming being excluded from said dioptry adjusting lens groups.

BACKGROUND OF THE INVENTION

This application is based on and claims priority from JapaneseApplication No. HEI 2-335935 filed Nov. 30, 1990, the disclosure ofwhich is incorporated by reference herein.

The present invention relates to an afocal optical system for use withbinoculars and monoculars, particularly to a zooming optical systemcapable of changing magnification.

Throughout this specification, the terms "group" and "component" areused interchangeably to refer to a structure comprising at least onelens element.

Eyepiece optical systems such as binoculars are often provided with adioptry adjustment capability for adjusting the focus in accordance withthe eyesight of the user. With zooming optical systems which are capableof adjusting the magnification (focal length), a reference dioptry whichdoes not change with the magnification is determined at the designstage.

If there is even a partial overlap between the lens group movable fordioptry adjustment and the lens group movable for zooming, the change indioptry due to zooming cannot be suppressed for all dioptries. Underthese circumstances, the dioptry most commonly used is specified as areference, and the system is designed such that zooming will cause nochange in dioptry at least in the case where the system is set for thereference dioptry. Hence, there will be no change in dioptry due tomagnification alterations if the system is set for the referencedioptry. However, if the system is set for values other than thereference dioptry, magnification alterations will cause changes indioptry, and another dioptry adjustment becomes necessary.

FIG. 21 shows a conventional zooming optical system. An objectiveoptical unit that is positioned closer to the object than a field ring Sis composed of a fixed first lens group G1 and a second lens group G2movable for zooming, whereas an eyepiece optical unit positioned closerto the eye than the field ring S is composed of a third lens group G3movable for zooming and a fourth lens group G4 that is fixed duringzooming. Dioptry adjustment is effected by moving altogether the threelens groups enclosed with a dashed line, i.e., the second lens group G2,the third lens group G3 and the fourth lens group G4.

A problem with this prior art zooming optical system is that the lensgroups movable for dioptry adjustment experience a great change in focallength during zooming, since those dioptry adjusting lens groups containall of the lens groups G2 and G3 which have a zooming capability. Theeyesight mismatch decreases with decreasing change in the focal lengthsof the dioptry adjusting groups, so a great eyesight mismatch willinevitably occur in the conventional system.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide and afocalzooming optical system that is capable of substantially preventing theoccurrence of eyesight mismatch during zooming.

This and other objects of the invention are attained by an afocalzooming optical system comprising a plurality of lens groups orcomponents, in which some of the lens groups movable along the opticalaxis for zooming are included in the dioptry adjusting lens groupsmovable for dioptry adjustment, and others of the lens groups movablefor zooming being excluded from the dioptry adjusting lens groups.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be more clearly understood from the followingdescription in conjunction with the accompanying drawings, in which:

FIG. 1 is a schematic diagram illustrating the operation of an afocalzooming optical system according to the present invention;

FIG. 2 is a graph comparing eyesight mismatch for the case of aconventional lens system and the system of FIG. 1;

FIGS. 3, 5 and 7 illustrate the composition of the lens system accordingto a first embodiment of the present invention in low magnification,moderate magnification and high magnification positions, respectively;

FIGS. 4, 6 and 8 are graphs plotting the aberration curves for the lenssystems as illustrated in FIGS. 3, 5 and 7, respectively;

FIGS. 9, 11 and 13 illustrate the composition of the lens systemaccording to a second embodiment of the present invention in lowmagnification, moderate magnification and high magnification positions,respectively;

FIGS. 10, 12 and 14 are graphs plotting the aberration curves for thelens systems as illustrated in FIGS. 9, 11 and 13, respectively;

FIGS. 15, 17 and 19 illustrate the composition of the lens systemaccording to a second embodiment of the present invention in lowmagnification, moderate magnification and high magnification positions,respectively;

FIGS. 16, 18 and 20 are graphs plotting the aberration curves for thelens systems as illustrated in FIGS. 15, 17 and 19, respectively; and

FIG. 21 is a schematic diagram showing a conventional afocal zoomingoptical system.

In the drawings, ER is the eye ring, ERφ means a diameter of the eyering, B is the angle defined by the optical axis and the principal rayof the exit pupil light flux.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will now be described with reference to FIGS.1-20, with the operating theory of the present invention being firstdescribed.

An afocal zooming optical system such as a monocular or binocular havinga zooming capability is composed of a plurality of lens groups with atleast part of the system being moved along the optical axis for zooming,and with at least a part of the system being moved along the opticalaxis for dioptry adjustment. If the lens groups movable for zooming aredefined as "zooming lens groups" whereas those movable for dioptryadjustment are defined as a "dioptry adjusting lens groups", the twosets of groups overlap at least partially. In other words, at least onelens group serves both as a zooming group and as a dioptry adjustinggroup.

As already mentioned, a dioptry set for values other than a referencedioptry will change upon zooming. If the amount of change in dioptry(eyesight mismatch) that occurs upon zooming from a low to a highmagnification is expressed by ΔDI, its value can be determined by:

    ΔDI=(DIW-DIO)·(fxw/fxt).sup.2               (1)

where DIW is the dioptry set for low magnification, DIO is the referencedioptry, fxw is the composite focal length of the dioptry adjusting lensgroups at low magnification, and fxt is the composite focal length ofthe dioptry adjusting lens group at high magnification.

As one can see from equation (1), the eyesight mismatch that occurs uponzooming can be suppressed or held at a low value by reducing the changein the composite focal length of the dioptry adjusting lens groups whichare moved for dioptry adjustment.

Hence, in the afocal zooming optical system of the present invention, atleast one of the zooming lens groups is included as a dioptry adjustinglens group movable for dioptry adjustment, whereas at least one of thezooming lens groups is not included as a dioptry adjusting lens group.Compared to the case where all of the zooming lens groups are includedas dioptry adjusting lens groups, the system of the present inventionhas the advantage that the focal length of the dioptry adjusting lensgroup experiences only a small change upon zooming, whereby possibleeyesight mismatch can be reduced to a small level.

It is possible to perform the dioptry adjustment only with the fourthlens group G4. It is, however, possible to move the third and fourthgroups G3, G4 for the dioptry adjustment. In this case, the amount ofmovement of the lens groups for the adjustment may be small.

FIG. 1 shows a four-group zoom lens system as an embodiment of thepresent invention. An objective optical unit that is positioned closerto the object than a field ring S is composed of a fixed first lensgroup G1 and a second lens group G2 movable for zooming. An eyepieceoptical unit that is positioned closer to the image than the field ringS is composed of a third lens group G3 movable for zooming and a fourthlens group G4 that is fixed during zooming. Dioptry adjustment iseffected by moving in unison the two lens groups enclosed with a dashedline, i.e., the third lens group G3 and the fourth lens group G4. Hence,in accordance with the present invention, the third lens group G3 whichis a zooming lens group is also included as a dioptry adjusting lensgroup, but the second lens group G2 which is also a zooming lens groupis not included as a dioptry adjusting lens group.

FIG. 2 compares the eyesight mismatch between two cases: one being suchthat dioptry adjustment is effected with a four-group zoom lens systemby the method illustrated in FIG. 1, and the other being the case wheredioptry adjustment is effected with a zoom lens system of the samecomposition by the conventional method shown in FIG. 21. The resultobtained by the embodiment of FIG. 1 is indicated by solid lines, withthe lens configuration corresponding to Lens Composition 2 set forthlater herein. The result obtained by the conventional method isindicated by dashed lines.

As one can see from FIG. 2, the system of the present invention in whichat least one of the zooming lens groups is not included as a dioptryadjusting lens group has the advantage that the eyesight mismatch can bereduced to a smaller level than in the case where all of the zoominglens groups are included as dioptry adjusting lens groups.

Three specific examples of the lens composition that can be adopted torealize the optical system described above are set forth below. In theseexamples, the reference dioptry is set at -1 diopter.

Lens Composition 1

FIGS. 3, 5 and 7 show a first embodiment of the lens composition for thezooming optical system of the present invention, at low, moderate andhigh magnifications, respectively.

Specific numerical data for the system are given in Table 1, wherein ris the radius of curvature of an individual lens surface, d is the lensthickness or air space, n is the refractive index of a lens, and ν isthe Abbe number of a lens. The fourth to the seventh surfaces are thoseof erecting prisms.

The magnification is altered by changing d7, d9 and d14, and thenumerical data for the respective alterations are given in Table 2,wherein f0 is the focal length of the objective optical unit, fe is thefocal length of the eyepiece optical unit, and ω is the half view angle.As already mentioned, the reference dioptry is -1 diopter.

The aberration curves obtained with lens composition 1 are plotted inFIG. 4 for low magnification, in FIG. 6 for moderate magnification andin FIG. 8 for high magnification.

                  TABLE 1                                                         ______________________________________                                        Surface                                                                       No.       r        d           n     ν                                     ______________________________________                                        1         63.811   4.79        1.51633                                                                             64.1                                     2         -38.439  1.31        1.62004                                                                             36.3                                     3         -117.465 23.76                                                      4         ∞  33.26       1.56883                                                                             56.3                                     5         ∞  1.58                                                       6         ∞  30.09       1.56883                                                                             56.3                                     7         ∞  variable                                                   8         -70.480  1.31        1.51633                                                                             64.1                                     9         26.398   variable                                                   10        -322.719 1.31        1.80518                                                                             25.4                                     11        11.419   5.82        1.71300                                                                             53.8                                     12        -23.749  0.17                                                       13        55.560   3.72        1.51633                                                                             64.1                                     14        -21.238  variable                                                   15        35.161   2.56        1.51633                                                                             64.1                                     16        -54.737                                                             ______________________________________                                    

                  TABLE 2                                                         ______________________________________                                        Low Magni-      Moderate Mag-                                                                             High Magni-                                       fication        nification  fication                                          ______________________________________                                        f0     100.000      133.95      158.93                                        fe     16.69        15.02       13.36                                         ω                                                                              3.50° 2.56°                                                                              2.08°                                  d7     23.27        14.41       10.30                                         d9     7.03         21.13       31.71                                         d14    12.28        7.04        0.57                                          ______________________________________                                    

When dioptry adjustment is effected by the method shown in FIG. 1, thedioptry present for the low magnification will vary at the moderate andhigh magnifications as shown in Table 3. Table 4 shows the numericaldata obtained in the case where the same optical system is used, butwhere dioptry adjustment is by the prior art method shown in FIG. 21. InTables 3 and 4, symbol fx denotes the composite focal length of thedioptry adjusting lens groups.

                  TABLE 3                                                         ______________________________________                                        DIOPTRY fx                                                                    (In Diopters)                                                                 Low Magni-    Moderate Mag-                                                                             High Magni-                                         fication      nification  fication                                            ______________________________________                                        -4.0          -4.7        -5.7                                                -2.0          -2.2        -2.6                                                -1.0          -1.0        -1.0                                                0.0           +0.2        +0.6                                                +2.0          +2.7        +3.7                                                16.69         15.02       13.36                                               ______________________________________                                    

                  TABLE 4                                                         ______________________________________                                        DIOPTRY fx                                                                    (In Diopters)                                                                 Low Magni-    Moderate Mag-                                                                             High Magni-                                         fication      nification  fication                                            ______________________________________                                        -4.0          -7.7        -12.9                                               -2.0          -3.2        -5.0                                                -1.0          -1.0        -1.0                                                0.0           +1.2        +3.0                                                +2.0          +5.7        +10.9                                               15.89         10.64       7.96                                                ______________________________________                                    

Lens Composition 2

FIGS. 9, 11 and 13 show a second embodiment of the lens composition forthe zooming optical system of the present invention, at low, high andmoderate magnifications, respectively. Specific numerical data for thesystem are given in Table 5. In Lens Composition 2, the magnification isaltered by changing d7, d9 and d14, and the numerical data for therespective alterations are given in Table 6.

The aberration curves obtained with Lens Composition 2 are plotted inFIGS. 10, 12 and 14 for low, moderate and high magnifications,respectively.

                  TABLE 5                                                         ______________________________________                                        Surface                                                                       No.       r        d           n     ν                                     ______________________________________                                        1         57.232   4.99        1.51633                                                                             64.1                                     2         -36.823  1.45        1.62004                                                                             36.3                                     3         -116.590 25.89                                                      4         ∞  29.93       1.56883                                                                             56.3                                     5         ∞  1.81                                                       6         ∞  29.93       1.56883                                                                             56.3                                     7         ∞  variable                                                   8         -41.540  1.18        1.51633                                                                             64.1                                     9         26.168   variable                                                   10        55.235   1.18        1.80518                                                                             25.4                                     11        10.857   5.62        1.71300                                                                             53.8                                     12        -22.194  0.36                                                       13        145.117  2.63        1.51633                                                                             64.1                                     14        -26.719  variable                                                   15        19.391   2.36        1.51633                                                                             64.1                                     16        141.943                                                             ______________________________________                                    

                  TABLE 6                                                         ______________________________________                                        Low Magni-      Moderate Mag-                                                                             High Magni-                                       fication        nification  fication                                          ______________________________________                                        f0     100.00       131.84      155.83                                        fe     16.45        14.68       13.14                                         ω                                                                              2.67° 1.94°                                                                              1.58°                                  d7     14.31        7.77        4.61                                          d9     10.23        22.23       31.36                                         d14    13.37        7.90        1.93                                          ______________________________________                                    

When dioptry adjustment is effected by the method shown in FIG. 1, thedioptry preset for the low magnification will vary at the moderate andhigh magnifications as shown in Table 7. Table 8 shows the numericaldata obtained in the case where the same optical system is used, butwhere dioptry is adjusted by the prior art method shown in FIG. 21. InTables 7 and 8, symbol fx denotes the composite focal length of thedioptry adjusting lens groups.

                  TABLE 7                                                         ______________________________________                                        DIOPTRY fx                                                                    (In Diopters)                                                                 Low Magni-    Moderate Mag-                                                                             High Magni-                                         fication      nification  fication                                            ______________________________________                                        -4.0          -4.8        -5.7                                                -2.0          -2.3        -2.6                                                -1.0          -1.0        -1.0                                                0.0           +0.3        +0.6                                                +2.0          +2.8        +3.7                                                16.45         14.68       13.14                                               ______________________________________                                    

                  TABLE 8                                                         ______________________________________                                        DIOPTRY fx                                                                    (In Diopters)                                                                 Low Magni-    Moderate Mag-                                                                             High Magni-                                         fication      nification  fication                                            ______________________________________                                        -4.0          -7.6        -12.5                                               -2.0          -3.2        -4.8                                                -1.0          -1.0        -1.0                                                0.0           +1.2        +2.8                                                +2.0          +5.6        +10.5                                               14.52         9.80        7.41                                                ______________________________________                                    

Lens Composition 3

FIGS. 15, 17 and 19 show a third example of the lens composition for thezooming optical system of the present invention at low, moderate andhigh magnifications, respectively. Specific numerical data for thesystem are given in Table 9. In Lens Composition 3, two of the five lenselements in the eyepiece optical unit, namely, the first lens positionedclosest to the object and the fourth lens, are plastic lenses.

The aberration curves obtained with Lens Composition 3 are plotted inFIGS. 16, 18 and 20 for low magnification, moderate magnification andhigh magnification, respectively.

                  TABLE 9                                                         ______________________________________                                        Surface                                                                       No.       r        d           n     ν                                     ______________________________________                                        1         64.573   5.24        1.51633                                                                             64.1                                     2         -33.786  1.52        1.62004                                                                             36.3                                     3         -95.352  28.57                                                      4         ∞  32.38       1.56883                                                                             56.3                                     5         ∞  1.91                                                       6         ∞  28.57       1.56883                                                                             56.3                                     7         ∞  variable                                                   8         -160.979 1.24        1.492 57.4                                     9         14.802   variable                                                   10        -63.592  1.24        1.80518                                                                             25.4                                     11        14.263   6.57        1.71300                                                                             53.8                                     12        -17.104  0.38                                                       13        50.744   3.52        1.492 57.4                                     14        -27.452  variable                                                   15        24.422   2.67        1.51633                                                                             64.1                                     16        186.044                                                             ______________________________________                                    

                  TABLE 10                                                        ______________________________________                                        Low Magni-      Moderate Mag-                                                                             High Magni-                                       fication        nification  fication                                          ______________________________________                                        f0     100.000      136.95      165.18                                        fe     16.66        15.28       13.96                                         ω                                                                              2.67° 1.94°                                                                              1.58°                                  d7     12.35        5.78        2.75                                          d9     9.55         21.55       30.82                                         d14    12.51        7.07        0.84.                                         ______________________________________                                    

When dioptry adjustment is effected by the method shown in FIG. 1, thedioptry present for the low magnification will vary at the moderate andhigh magnifications as shown in Table 11. Table 12 shows the numericaldata obtained in the case where the same optical system is used, butwhere dioptry adjustment is by the prior art method shown in FIG. 21. InTables 11 and 12, symbol fx denotes the collective focal length of thedioptry adjusting lens groups.

                  TABLE 11                                                        ______________________________________                                        DIOPTRY fx                                                                    (In Diopters)                                                                 Low Magni-    Moderate Mag-                                                                             High Magni-                                         fication      nification  fication                                            ______________________________________                                        -4.0          -4.6        -5.3                                                -2.0          -2.2        -2.4                                                -1.0          -1.0        -1.0                                                0.0           +0.2        +0.4                                                +2.0          +2.6        +3.3                                                16.66         15.28       13.96                                               ______________________________________                                    

                  TABLE 12                                                        ______________________________________                                        DIOPTRY fx                                                                    (In Diopters)                                                                 Low Magni-    Moderate Mag-                                                                             High Magni-                                         fication      nification  fication                                            ______________________________________                                        -4.0          -7.7        -12.8                                               -2.0          -3.2        -4.9                                                -1.0          -1.0        -1.0                                                0.0           +1.2        +2.9                                                +2.0          +5.7        +10.8                                               14.88         9.93        7.50                                                ______________________________________                                    

As described above, the variations in the focal length of the dioptryadjusting lens groups that occur during zooming can be held to smalllevels in the system of the present invention, which hence ischaracterized by a very small amount of eyesight mismatch that occursduring zooming.

What is claimed is:
 1. An afocal zooming optical system comprising aplurality of lens components, wherein at least a first and a second ofsaid plurality of lens components are movable along an optical axis forchanging a magnification of the optical system and said first lenscomponent is moved while said second lens component remains stationaryfor dioptry adjustment without changing a magnification of the opticalsystem, wherein at least a third of said plurality of lens components ismovable for dioptry adjustment and is not movable for changing amagnification ,of the optical system.
 2. An afocal zooming opticalsystem comprising a field ring, an objective optical unit positionedcloser to the object than said field ring for defining the field rangeand an eyepiece optical unit positioned closer to the eye than saidfield ring, with at least part of the eyepiece optical unit being movedfor changing a magnification of the optical system whereas said eyepieceoptical unit is moved en masse along the optical axis while all portionsof said objective optical unit remain stationary for dioptry adjustmentwithout changing the magnification of the optical system.
 3. An afocalzooming optical system comprising a zooming lens component movable alongthe optical axis for changing a magnification of the optical system anda fixed lens component not movable when a magnification of the opticalsystem is changed, with a positive lens unit in said zooming lenscomponent being moved together with a lens unit in said fixed lenscomponent that is positioned closer to the eye than said positive lensunit for dioptry adjustment without changing a magnification of theoptical system.
 4. An afocal zooming optical system comprising: in orderfrom the object side,a first lens unit having a positive power and fixedduring operation for changing a magnification of the optical system anddioptry adjustment; a second lens unit having a negative power, saidsecond lens unit being movable in an optical axis direction duringoperation for changing a magnification of the optical system but fixedduring dioptry adjustment; a third lens unit having a positive power andmoveable in the optical axis direction during operation for changing amagnification of the optical system and dioptry adjustment; and a fourthlens unit having a positive power, said fourth lens unit being fixedduring operation for changing a magnification of the optical system butmoveable in the optical axis direction during dioptry adjustment.
 5. Theafocal zooming optical system according to claim 4, wherein a field ringis interposed between said second lens unit and said third lens unit.